Orthogonal frequency-division multiplexing (OFDM) is a method of encoding digital data on multiple carrier frequencies. The OFDM scheme is currently deployed in broadband multicarrier communications. However, OFDM suffers from high out of band (OOB) radiation due to the use of a square pulse (e.g., a sinc function in frequency domain) on each subcarrier. A guard band can be used to avoid interference between two bands due to OOB radiation. Filtered OFDM (F-OFDM) is a scheme in which a filtering is applied to a sequence of OFDM symbols to reduce OOB radiation. The F-OFDM scheme has benefits of OFDM, e.g., simple equalization, channel estimation, and suitability for multiple-input and multiple-output (MIMO) transmissions. OFDM/Offset Quadrature Amplitude Modulation (OQAM) is a filter bank multicarrier (FBMC) scheme which uses a time/frequency localized pulse shaping over each subcarrier to yield a spectrally contained waveform. This scheme provides a relatively well contained spectrum and is suitable for synchronous/asynchronous communications. Another other FBMC schemes can also be considered. In the OFDM scheme, the guard band is not exploited for data transmission, which results in loss of spectral efficiency. There is a need for a scheme that allows opportunistic radio communications and improves spectral efficiency for synchronous/asynchronous communications.